September 23rd...

 

"Here's Lucy" - "Mod, Mod Lucy"

September 23, 1968 (55 years)

pictured above: Lucille Ball and Gale Gordon

"Matlock" - "The Judge"

September 23, 1986 (37 years)

pictured above: Andy Griffith as Ben Matlock with guest star Don Knotts

The series began as a 100-minute television special "Diary of a Perfect Murder" which originally aired on March 3, 1986.  It began as a weekly series on the date listed above.